Agitation systems in stirred slurry reactors and storage tanks often include a tickler (kicker) impeller as part of the agitation system. The tickler impeller is mounted on an agitator shaft and located at close proximity to the tank bottom. The purpose of the tickler is to keep the solids suspended and eliminate settling of the solids at the bottom of the tank. Ticklers are normally pitch blade turbines (PBTs) or flat blade turbines (FBTs), see FIGS. 1 and 2, respectively.
In relation to a main impeller, which agitates solids in a liquid medium, the tickler is a smaller agitator located in a spaced relation below the main impeller. While draining the tank, particularly after the slurry level has receded below a main impeller, efficiency of the tickler for solids suspension is critical to avoid solids deposition, pump starvation, and choking of the flow due to plugging of the pump suction line. Typically, PBT and FBT ticklers function near the bottom of the tank as radial impellers which tend to throw the slurry out towards the wall of the tank, i.e. away from the central nozzle or drain. As a result, solids can stick to the wall and necessitate the extra work of removal by pressure spraying them from the wall. Pump starvation and long discharge times also can result from discharge nozzle starvation near the end of draining the slurry from the tank.